Positioning device and positioning system

ABSTRACT

A positioning device includes a processor configured to calculate a first neighboring time at which the mobile device becomes closest to a first base station in the plurality of base stations based on the received signal strength data and a second neighboring time at which the mobile device becomes closest to a second base station of the plurality of base stations, and convert the relative movement data in the second storage device into position coordinates data specifying an absolute position of the mobile device in an absolute coordinate system using the first base station as a reference point from the first neighboring time to the second neighboring time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/927,138, filed on Mar. 21, 2018, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2017-134784,filed Jul. 10, 2017, the entire contents of each of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a positioning deviceand a positioning system.

BACKGROUND

In an autonomous pedestrian navigation system that uses a pedestriandead reckoning (PDR) technique, in which a position of a person or otherobject is detected and then a trajectory of the person or object ismonitored or tracked based on detected changes in position. In the PDRtechnique, a moving direction and a moving distance can be detected byan acceleration sensor, a gyro sensor (also referred to as an angularvelocity sensor), or a geomagnetic sensor (also referred to as anelectronic compass).

In the PDR technique, a position of the person or object is measuredrelative to an arbitrary base point. That is, the position isrepresented according to a relative coordinate system. Therefore, forexample, when the trajectory of person or object is to be displayed on amap using an absolute coordinate system, it is necessary to convertpositions in the relative coordinate system (also referred to asrelative coordinates) into coordinates in an absolute coordinate system(also referred to as absolute coordinates) for representation on themap.

In general, a person or an object carries a mobile station such as amobile phone or mobile computer that can be connected to a mobilenetwork. In communicating with the mobile network, the mobile stationreceives radio waves transmitted from a fixed-location transmissionstation. When the radio waves are received at the mobile station, theabsolute coordinates of the transmission station can be used indetermining the current position of the mobile station carried by theperson or object. For example, the positioning device obtains a positionin the absolute coordinate system, that is, a so-called absoluteposition, from a position measurement result obtained by a PDR techniquethat uses the coordinates of the fixed-location transmission station asa base point.

However, there may be inaccuracies in determining coordinatesrepresenting the current position of the mobile station in this manner.When a distance that radio waves travel from the transmission station tothe mobile station is long, there is a possibility that the coordinatesof the mobile station specified in the radio waves from the transmissionstation may not correspond to an actual position of the mobile stationat the time of receiving the radio waves. That is, an absolute positionof the mobile station in the absolute coordinate system set at thetransmission station specified in the received radio wave is deviatedfrom an actual position of the mobile station, and such deviationsbecome large as a distance between the mobile station and thetransmission station becomes large. However, if the permissible distancebetween the mobile station and the transmission station is shortened orrestricted, then there may be instances in which the mobile stationcannot utilize radio waves from a fixed-location transmission stationand thus the current coordinates of the mobile station cannot bespecified at all times.

In the related art, there is a technique in which a predeterminedoperation is performed by the mobile station when the mobile stationcomes closest to the transmission station, and the absolute coordinatesare set according to signals received from the fixed transmissionstation after the predetermined operation is completed. Also, there is atechnique in which a threshold value of the received signal strengthfrom the transmission station is set in advance within the mobilestation and the absolute coordinates from the fixed transmission stationare set according to when the received signal strength exceeds thethreshold value. However, the first technique is cumbersome because, ingeneral, a non-autonomous operation by a person is required and thus useis restricted because human intervention is required. In the secondtechnique, the received signal strength from the fixed transmissionstation may exceed the threshold value at an unexpected place distantfrom the fixed transmission station and in such a case, accuracy ofpositioning will be decreased.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall configuration diagram of a positioning systemaccording to an embodiment.

FIG. 2 depicts an example of data stored in a first table of FIG. 1.

FIG. 3 depicts an example of data stored in a second table of FIG. 1.

FIG. 4 depicts an example of data stored in a third table of FIG. 1.

FIG. 5 depicts an example of data stored in a fourth table of FIG. 1.

FIG. 6 is a schematic diagram of an example movement of a positioningtarget.

FIG. 7 is a flowchart of main information processing executed by aprocessor of a positioning server.

FIG. 8 is another flowchart of main information processing executed by aprocessor of a positioning server.

FIG. 9 is an example of a trajectory display screen.

FIG. 10 is another example of a trajectory display screen.

DETAILED DESCRIPTION

In general, according to one embodiment, a positioning device includes afirst storage device having stored therein received signal strength datain time series according to mobile device data, the mobile device dataincluding current time information and a received signal strengthindicator according to a signal strength between a mobile device andeach of a plurality of base stations, a second storage device havingstored therein relative movement data of the mobile device in timeseries within a relative coordinate system, and a processor configuredto calculate a first neighboring time at which the mobile device becomesclosest to a first base station in the plurality of base stations basedon the received signal strength data in the first table, and then, asecond neighboring time when the mobile device becomes closest to asecond base station of the plurality of base stations, and convert therelative movement data in the second table into position coordinatesdata specifying an absolute position of the mobile device in an absolutecoordinate system having the first base station as a base point from thefirst neighboring time until the second neighboring time.

In the example embodiments described below, a positioning device candetect an absolute position of a positioning target with highreliability without requiring a user's operation.

FIG. 1 is an overall configuration diagram of a positioning system 100according to an embodiment. The positioning system 100 tracks a positionof a positioning target, such as a person or an object, that moveswithin a predetermined positioning area or zone, for example, inside abuilding, such as a factory, a warehouse, or an office, or within a sitein which a building or a facility is provided. The positioning system100 includes multiple base stations (also referred to as transmissionstations) 10 (individually labeled as 10A, 10B, and 10C in FIG. 1), amobile station 20, and a positioning server 30 (also referred to as apositioning device).

The base stations 10 are fixed-location stations that are spaced apartfrom each other so as to be distributed within the positioning area. Assuch, each base station 10 is at a fixed location and thus the absolutecoordinates of each base station are known. The number of the basestations 10 is not particularly limited to three. In consideration ofcircumstances of the positioning area, such as presence or absence of anobstacle, or the like, an appropriate number of the base stations 10 canbe disposed at various positions within the positioning area.

The base station 10 functions as a transmitting device of a beaconsignal. That is, each base station 10 transmits a predetermined uniquebeacon signal. Typically, the base station 10 is a beacon terminal thatrepeatedly transmits a Bluetooth® beacon signal according to theBluetooth low energy (BLE) standard. The base station 10 may alsotransmit a beacon signal other than a Bluetooth® beacon signal. Thebeacon signal includes a beacon ID as identification information forspecifying each base station 10. The beacon ID is unique information inwhich a different value is set for each base station 10.

A base station 10 includes at least a processor 11, a memory 12, and atransmission/reception circuit 13, and these components are connected toeach other by a system transmission path 14 such as an address bus or adata bus. The base station 10 can be a computer having the processor 11and the memory 12 connected by the system transmission path 14.

The processor 11 corresponds to a central processing unit of thecomputer. The processor 11 may control various sub-components to realizethe various functions of the base station 10 according to an operatingsystem and an application program executed thereon.

The memory 12 corresponds to a storage portion of the computer. Thememory 12 includes a nonvolatile memory area and a volatile memory area.The memory 12 stores the operating system and the application program inthe nonvolatile memory area. The memory 12 stores data necessary for theprocessor 11 functions in the nonvolatile memory area or the volatilememory area. The memory 12 uses the volatile memory area as a work areawhere data may be rewritten by the processor 11. The memory 12 uses thenonvolatile memory area as a storage portion for the beacon ID.

The transmission/reception circuit 13 wirelessly transmits a beaconsignal including the beacon ID, according to a short-range wirelesscommunication standard such as the BLE.

The mobile station 20 is a wireless communication terminal that can becarried by a positioning target, such as a person or other object, andmoves together with the positioning target. The mobile station 20functions as a receiving device for the beacon signal. That is, when themobile station 20 exists within a radio wave arrival area of the beaconsignal transmitted from the base station 10, the mobile station 20 canreceive the beacon signal. When the beacon signal is received, themobile station 20 detects the beacon ID in the beacon signal. Further,the mobile station 20 measures reception strength of the beacon signal,referred to as a received signal strength indication (RSSI). The mobilestation 20 generates beacon data in which the beacon ID and the RSSIvalue are paired.

When the mobile station 20 is within transmission range of a pluralityof base stations 10, the mobile station 20 receives the beacon signalstransmitted from each of the base stations 10, respectively, andgenerates beacon data for each received beacon signal.

The mobile station 20 can measure a movement of the positioning targetusing the PDR technique. That is, the mobile station 20 includes anacceleration sensor, a gyro sensor, a geomagnetic sensor, or the like,and measures a direction including an angle and a distance of themovement of the positioning target, that is, a moving direction and amoving distance in real time, based on information from the sensors. Themobile station 20 obtains two-dimensional coordinates representing theposition of the positioning target, referred to as relative coordinates(PDRx, PDRy) over time. The relative coordinates are represented in therelative coordinate system having a position of the positioning targetat a start time is set as a base point (0,0), and coordinate changes arederived based on time-integrated data of the moving direction and themoving distance of the positioning target. Each time when the relativecoordinates (PDRx, PDRy) of the positioning target are obtained, themobile station 20 generates data (hereinafter, referred to as “relativemovement data”) in the relative coordinate system relating the movementof the positioning target. The relative movement data includes thecurrent relative coordinates (PDRx, PDRy) and a moving direction and amoving distance from the previous relative coordinates obtained one timeunit ago.

The mobile station 20 includes at least a processor 21, a memory 22, atransmission/reception circuit 23, a clock 24, a sensor unit 25, and awireless unit 26. These components are connected to each other by asystem transmission line 27 such as an address bus or a data bus. Themobile station 20 is a computer having the processor 21 and the memory22 connected to each other by the system transmission line 27.

The processor 21 corresponds to a central processing unit of a computer.The processor 21 controls each unit to realize various functions of themobile station 20, according to an operating system and an applicationprogram.

The memory 22 corresponds to a storing portion of the computer. Thememory 22 includes a nonvolatile memory area and a volatile memory area.The memory 22 stores the operating system and the application program inthe nonvolatile memory area. The memory 22 stores data necessary for theprocessor 21 to control each unit in the nonvolatile memory area or thevolatile memory area. The memory 22 uses the volatile memory area as awork area where data is appropriately rewritten by the processor 21. Thememory 22 uses the nonvolatile memory area as a storing portion of amobile station ID. The mobile station ID is unique information in whicha different value is set for each mobile station 20. The mobile stationID functions as identification information of the mobile station 20.

The transmission/reception circuit 23 receives a beacon signaltransmitted from a base station 10 according to a short-range wirelesscommunication standard such as the BLE. The transmission/receptioncircuit 23 includes a circuit for measuring the RSSI, which is thereception strength of the beacon signal.

The clock 24 provides the current date and time.

The sensor unit 25 includes an acceleration sensor, a gyro sensor, ageomagnetic sensor, or the like, which are sensors for the PDR. Theacceleration sensor measures acceleration of the mobile station 20. Thegyro sensor measures rotational angular velocity of the mobile station20. The geomagnetic sensor measures a direction of a terrestrialmagnetic field around the mobile station 20 and measures the azimuth ofthe mobile station 20 relative to, for example, magnetic North.

The wireless unit 26 performs wireless communication with an accesspoint 41 on a network 40 according to the local area network (LAN)standard such as IEEE 802.15, IEEE 802.11, or IEEE 802.3. Specifically,the wireless unit 26 wirelessly transmits mobile station data to thepositioning server 30 every one second in accordance with the clock 24,for example. The mobile station data includes the mobile station ID, thetime measured by the clock 24, beacon data at the measured time, andrelative movement data at the measured time.

As the mobile station 20 having such a configuration, a portableinformation terminal such as a smart phone, a mobile phone, a tabletterminal, or a notebook computer can be typically used.

The access point 41 is disposed at an appropriate position in thepositioning area so that mobile station data transmitted from the mobilestation 20 can be received from any location in the positioning area.The network 40 transmits mobile station data received by the accesspoint 41 to the positioning server 30. The network 40 is, for example, awireless network conforming to the WiFi® standard or a mobilecommunication network.

The positioning server 30 performs position measurement of the mobilestation 20 specified by the mobile station ID included in the mobilestation data, based on the mobile station data received through thenetwork 40. In other words, the positioning server 30 performs positionmeasurement of the positioning target which carries the mobile station20 specified by the mobile station ID.

The positioning server 30 includes at least a processor 31, a mainmemory 32, an auxiliary storage device 33, an input device 34, a displaydevice 35, and a communication circuit 36. These components areconnected to each other by a system transmission line 37 such as anaddress bus or a data bus. The positioning server 30 is a computerhaving the processor 31, the main memory 32, and the auxiliary storagedevice 33 connected to each other by the system transmission line 37.

The processor 31 corresponds to a central unit of the computer. Theprocessor 31 controls each unit to realize various functions as thepositioning server 30, according to an operating system and anapplication program.

The main memory 32 corresponds to a storing portion of the computer. Themain memory 32 includes a nonvolatile memory area and a volatile memoryarea. The main memory 32 stores the operating system and the applicationprogram in the nonvolatile memory area. The main memory 32 stores datanecessary for the processor 31 to control each unit in the nonvolatilememory area or the volatile memory area. The main memory 32 uses thevolatile memory area as a work area where data is appropriatelyrewritten by the processor 31.

The auxiliary storage device 33 corresponds to an auxiliary storingportion of the positioning server 30. For example, an electric erasableprogrammable read-only memory (EEPROM), a hard disc drive (HDD), a solidstate drive (SSD), and the like are used as the auxiliary storage device33. In the auxiliary storage device 33, a first table 331, a secondtable 332, a third table 333, and a fourth table 334 are formed. Thefirst to fourth tables 331, 332, 333, and 334 are formed respectivelyfor one positioning target. That is, when multiple positioning targetsare present, the first to fourth tables 331, 332, 333, and 334 areformed for each positioning target.

The input device 34 and the display device 35 function as a userinterface device that are responsible for information transmissionbetween the positioning server 30 and a user of the server. The inputdevice 34 is a touch panel, a mouse, a keyboard, or the like. Thedisplay device 35 is a liquid crystal display, an LED display, or thelike.

The communication circuit 36 is connected to the network 40 and capturesmobile station data received by the access point 41.

Next, the first to fourth tables 331, 332, 333, and 334 will bedescribed with reference to FIGS. 2 to 5.

FIG. 2 depicts an example of data stored in the first table 331. Asdepicted in FIG. 2, in the first table 331, pieces of beacon data, inwhich beacon IDs and values of RSSI are paired with each other, arestored in order of stronger RSSI from first place to third place inassociation with the time.

Each time when mobile station data is received from one mobile station20, the processor 31 acquires the time and beacon data included in themobile station data. When a plurality of pieces of beacon data areincluded in the mobile station data, the processor 31 compares the RSSIvalues included in the pieces of beacon data. The processor 31 selects abeacon ID in descending order of the RSSI value and sets the beacon IDand the value of RSSI together with the time included in the same mobilestation data in order from the first place in the first table 331. Whenthere is only one beacon data, the only one beacon data, together withthe time included in the same mobile station data, is set in the firsttable 331 as data of the first place. Here, the first table 331functions as a first storing unit.

FIG. 3 depicts an example of data stored in the second table 332. Asdepicted in FIG. 3, the relative coordinates (PDRx, PDRy), a movingdirection, and a moving distance are stored in the second table 332 inassociation with the time.

Each time when mobile station data is received from one mobile station20, the processor 31 acquires the time and relative movement dataincluded in the mobile station data. The processor 31 sets the relativecoordinates (PDRx, PDRy), the moving direction, and the moving distanceincluded in the relative movement data, together with the time includedin the same mobile station data, respectively, in the second table 332.Here, the second table 332 functions as a second storing unit.

FIG. 4 depicts an example of data stored in the third table 333. Asdepicted in FIG. 4, data of a first ID, an RSSI, an occupation ratio, asecond ID, a total angle sum, and a moving amount are stored in thethird table 333 in association with the time. The first ID, the RSSI,the occupation ratio, the second ID, the total angle sum, and the movingamount will be described later.

FIG. 5 depicts an example of data stored in the fourth table 334. Asdepicted in FIG. 5, two-dimensional coordinates in the absolutecoordinate system, referred to as absolute coordinates (X, Y) are storedin the fourth table 334 in association with the time. Specifically, inthe fourth table 334, the absolute coordinates (X, Y) obtained after therelative coordinates (PDRx, PDRy) representing the position of thepositioning target stored in FIG. 3 are converted into coordinates ofthe absolute coordinate system are stored.

FIG. 6 is a schematic diagram of an example movement of a positioningtarget 50 carrying the mobile station 20 within a positioning area 60.The base station 10A for which a beacon ID “435” is set, the basestation 10B for which a beacon ID “436” is set, and the base station 10Cfor which a beacon ID “437” is set are disposed in the positioning area60. Specifically, the base station 10A is disposed at a positionspecified by the absolute coordinates (X10, Y10) of the absolutecoordinate system in which the lower left of the positioning area 60 isset as the origin P(0, 0). Similarly, the base station 10B is disposedat a position specified by the absolute coordinates (X20, Y20) in thesame absolute coordinate system, and the base station 10C is disposed ata position specified by the absolute coordinates (X30, Y30) in the sameabsolute coordinate system. In the auxiliary storage device 33 of thepositioning server 30, position information indicating the absolutecoordinates of the base stations 10A, 10B, and 10C are stored in advancein association with the beacon ID of each of the base stations 10A, 10B,and 10C. Map information of the positioning area 60 is also stored inthe auxiliary storage device 33.

The origin P (0, 0) in the absolute coordinate system is not limited tothe position shown in FIG. 5. For example, the upper left or center ofthe positioning area 60 may be set as the origin P (0, 0). Each of thebase stations 10A, 10B, and 10C may be associated with identificationinformation for identifying each of the base stations 10A, 10B, and 10C,for example, a base station ID without associating position informationof each of the base stations 10A, 10B, and 10C with the beacon ID. Inthis case, a conversion table for storing the beacon ID and the basestation ID in association with each other and converting the beacon IDinto the base station ID is needed.

Hereinafter, an operation of the positioning system 100 will bedescribed based on a movement example of FIG. 6.

In the movement example of FIG. 6, the positioning target 50 the mobilestation 20 moves from the vicinity of the base station 10A at time“10:10:10”, passes through the vicinity of the base station 10B at time“10:10:17”, further passes through the vicinity of the base station 10Cat time “10:10:22”, and moves to a position depicted at time“10:10:24.”. Data of the first table 331 and the second table 332created by mobile station data wirelessly transmitted from the mobilestation 20 as needed according to such movement is depicted in FIGS. 2and 3.

At time “10:10:10”, the mobile station 20 receives the beacon signalincluding the beacon ID “435” with the largest RSSI “−80 dbm”, thebeacon signal including the beacon ID “436” with the second largest RSSI“−95 dbm”, and the beacon signal including the beacon ID “437” with thethird largest RSSI “−96 dbm”, as shown in the first table 331 of FIG. 2.Further, at the same time “10:10:10”, the positioning target 50 carryingthe mobile station 20 at a position of the relative coordinates (PDRx1,PDRy1) and moves 1.5 m in a direction of an angle of +10° and is presentas shown in the second table of FIG. 3

At time “10:10:11”, the mobile station 20 receives the beacon signalincluding the beacon ID “435” with the largest RSSI “−83 dbm”, thebeacon signal including the beacon ID “436” with the second largest RSSI“−92 dbm”, and the beacon signal including the beacon ID “437” with thethird largest RSSI “−96 dbm” as shown in the first table 331 of FIG. 2.Further, at the same time “10:10:11”, the positioning target 50 carryingthe mobile station 20 is present at a position of the relativecoordinates (PDRx2, PDRy2) and moves 1 m from the position of therelative coordinates (PDRx1, PDRy1) in the direction of an angle of −10°as shown in the second table 332 of FIG. 3.

The positions and the movements of the positioning target 50 describedabove can be similarly applied to other times after the times “10:10:10”and “10:10:11”. For example, at time “10:10:17”, the mobile station 20receives the beacon signal including the beacon ID “436” with thelargest RSSI “−79 dbm”, the beacon signal including the beacon ID “435”with the second largest RSSI “−93 dbm”, and the beacon signal includingthe beacon ID “437” with the third largest RSSI “−96 dbm” as shown inthe first table 331 of FIG. 2. At the same time “10:10:17”, thepositioning target 50 carrying the mobile station 20 is present at aposition of the relative coordinates (PDRx8, PDRy8) and moves 1 m from aposition of the relative coordinates (PDRx7, PDRy7) in the direction ofan angle of +40° as shown in the second table 332 of FIG. 3.

In a state where data depicted in FIGS. 2 and 3 are stored in the firsttable 331 and the second table 332, when an instruction to generate atrajectory of the positioning target is input through the input device34, the processor 31 executes information processing according to aprocedure depicted in flowcharts of FIG. 7 and FIG. 8. This informationprocessing follows a trajectory generation program stored in the mainmemory 32 or the auxiliary storage device 33. It should be noted thatthe particular processing steps described below are some possibleexamples of information processing for generating a trajectory of apositioning target 50 and do not limit the possible processing steps orthe like according to the present disclosure.

Initially, as Act 1, the processor 31 sets both a first flag F1 and asecond flag F2 to “0”. As Act 2, the processor 31 resets both a firstcounter n and a second counter t to “0”. A processing order of Act 1 andAct 2 may be reversed.

The first flag F1 is 1-bit data which holds “0” until a first record isrecorded in the third table 333 of FIG. 3 and the first flag F1 isupdated to “1” when the first record is recorded. The second flag F2 is1-bit data which holds “0” until the relative coordinates (PDRx, PDRy)stored in the second table 332 of FIG. 3 are converted into the absolutecoordinates (X, Y) and the second flag F2 is updated to “1” after theconversion. The first counter n counts a number of times when thepositioning target 50 comes closest to any of the base stations 10 (alsoreferred to as a neighboring time). The second counter t record thetime. The first flag F1, the second flag F2, the value of the firstcounter n, and the value of the second counter t are stored in thevolatile memory area of the main memory 32.

As Act 3, the processor 31 acquires a start time ST. The processor 31sets a value corresponding to the start time ST as an initial value ofthe second counter t. The start time ST is input through the inputdevice 34. In this operation example, the start time ST is set to“10:10:10”.

As Act 4, the processor 31 obtains the first ID, the RSSI, the totalangle sum, and the moving amount at time T and records the obtainedfirst ID, RSSI, total angle sum, and the moving amount in the thirdtable 333. Time T is the time corresponding to a value of the secondcounter t. The first ID is a beacon ID included in the beacon signalwhose the RSSI indicates the largest value at time T and the RSSI valueof the beacon signal is set in an RSSI area of the third table 333. Thefirst ID and the RSSI can be obtained from data at time T in the firsttable 331. The total angle sum is a value obtained by adding the angleof the positioning target 50 at time T to the total angle sum total ofthe record at time (T−1) in the third table 333. However, in a casewhere a record at time (T−1) does not exist in the third table 333, theangle of the positioning target 50 at time T is the total angle sum. Themoving amount is a moving amount of the positioning target 50 at time T.The angle and the moving amount of the positioning target 50 at time Tcan be obtained from data at time T of the second table 332.

In a case where the time T is the start time “10:10:10”, the record attime (T−1) does not exist in the third table 333. Accordingly, theprocessor 31 records “435” as the first ID, “−80” as the RSSI, “10” asthe total angle sum, and “1.5” as the moving amount, respectively, inthe third table 333 in association with the time “10:10:10”.

As Act 5, the processor 31 determines whether the first flag F1 is “0”or not. When it is determined that the first flag F1 is “0”, in Act 4,it is indicated that the first record is recorded in the third table333. When it is determined that the first flag F1 is “0” (YES in Act 5),as Act 6, the processor 31 records a predetermined value “0” as a secondID of the first record. As Act 7, the processor 31 updates the firstflag F1 with “1”. Thereafter, the processor 31 proceeds to Act 8.

In a case where the time T is the start time “10:10:10”, the first flagF1 is “0” at the time of Act 5. Accordingly, the processor 31 records“0” as the second ID in the record at time “10:10:10” of the third table333. The value recorded as the second ID in the first record of thethird table 333 is not limited to “0”. In short, a value with which theprocessor 31 can identify the first record may be available.

In Act 5, in a case where the first flag F1 is already updated with “1”(NO in Act 5), the processor 31 skips processing of Act 6 and Act 7 andproceeds to Act 8. That is, in a case where the second and subsequentrecords are recorded in the third table 333 in Act 4, the processor 31skips processing of Act 6 and Act 7 and proceeds to Act 8.

In Act 8, the processor 31 computes the occupation ratio. The occupationratio is a ratio of the base station for which the RSSI becomes thelargest within a time period retroacting from the current time T by apredetermined evaluation target time. In this operation example, theevaluation target time is set to 5 seconds. The beacon ID of the basestation having the largest RSSI within the evaluation time periodretroacting from the time T is recorded as the first ID in the thirdtable 333 for each time within the time period. The processor 31computes the occupation ratio from information of a first ID area of thethird table 333.

In a case where the time T is the start time “10:10:10”, a record beforetime “10:10:10” is not present in the first table 331. That is, as afirst ID which becomes a computation target of the occupation ratio,only the beacon ID of “435” of the base station 10A is present.Accordingly, in a case where the evaluation target time is set to 5seconds, the occupation ratio is 20% (⅕=0.2) of the base station 10A.The processor records “435:0.2” (“beacon ID:occupation ratio”), asoccupation ratio information, in the record at time “10:10:10” of thethird table 333.

As Act 9, the processor 31 determines whether the occupation ratio equalto or greater than a predetermined threshold value is calculated or not.In this operation example, the threshold value is set to 0.8 (80%). In acase where it is determined that the occupation ratio equal to orgreater than the threshold value is not calculated (NO in Act 9), as Act10, the processor 31 determines whether the second flag F2 is updatedwith “1” or not.

In a case where it is determined that the second flag F2 is updated with“1” (YES in Act 10), the processor 31 executes processing of Act 11 toAct 13. In a case where it is determined that the second flag F2 is notupdated with “1” (YES in Act 10), the processor 31 skips processing ofAct 11 and Act 12 and executes only processing of Act 13. Processing ofAct 11 and Act 12 will be described later. In Act 13, the processor 31counts up the second counter t by “1”.

As described above, in a case where the time T is “10:10:10”, theoccupation ratio equal to or greater than the threshold value is notcalculated. Also, the second flag F2 is “0”. Accordingly, the processor31 proceeds to Act 13 and counts up the second counter t by “1”.

When processing of Act 13 is ended, as Act 14, the processor 31determines whether or not an instruction to end positioning is input.The instruction to end the positioning is input through the input device34. In a case where it is determined that the instruction to end thepositioning is not input, the processor 31 returns to Act 4 and executesagain processing in and after Act 4.

That is, the processor 31 records “435” as the first ID, “−83” as theRSSI, “0” as the total angle sum, and “1.0” as the moving amount,respectively, in the third table 333 in association with the time“10:10:11” which corresponds to the value of the second counter t. Theprocessor 31 computes the occupation ratio. The first flag F1 is updatedwith “1” and thus, the processor 31 does not perform processing of Act 6and Act 7.

In a case where the time T is “10:10:11”, as the first ID which becomesthe computation target of the occupation ratio, only two beacon IDs of“435” of the base station 10A are present. Accordingly, in a case wherethe evaluation target time is set to 5 seconds, the occupation ratio is40% (⅖=0.4) of the base station 10A. The processor 31 records “435:0.4”as occupation ratio information in the record at time “10:10:11” in thethird table 333. Also, in this case, the occupation ratio does not reachthe threshold value and thus, the processor 31 proceeds to Act 13 andcounts up the second counter t. Thereafter, in a case where theinstruction to end positioning is not made, the processor 31 returns toAct 4 and executes processing in and after Act 4 again.

As a result, the processor 31 records “435” as the first ID, “−86” asthe RSSI, “435:0.6” as the occupation ratio, “−20” as the total anglesum, and “1.2” as the moving amount, respectively, in the third table333 in association with the time “10:10:12”. The processor 31 records“435” as the first ID, “−87” as the RSSI, “435:0.8” as the occupationratio, “−30” as the total angle sum, and “1.0” as the moving amount,respectively, in the third table 333 in association with the time“10:10:13”.

Here, the occupation ratio calculated at “10:10:13” is equal to orgreater than the threshold value. When it is determined that theoccupation ratio is equal to or greater than the predetermined thresholdvalue (YES in Act 9), the processor 31 proceeds to Act 21 of FIG. 8.That is, as Act 21, the processor 31 records the beacon ID “435” of thebase station whose occupation ratio is equal to or greater than thethreshold, as the second ID, in the record at time “10:10:13” of thethird table 333.

When processing of Act 21 is ended, as Act 22, the processor 31retrieves the second ID of the record, which is recorded in the thirdtable 333 in association with the time before time T, retroactively fromthe time T. As Act 23, the processor 31 determines whether or not asecond ID detected first is “0” or the same as the second ID recorded inthe third table 333 in association with the time T. Here, in a casewhere it is determined that a second ID detected first is “0” or thesame as the second ID recorded in the third table 333 in associationwith the time T (YES in Act 23), the processor 31 proceeds to Act 10 ofFIG. 7.

In the present operation example, at time “10:10:13”, the second IDdetected first from the third table 333 is “0” associated with the time“10:10:10”. Accordingly, the processor 31 proceeds to Act 10. At thispoint in time, the second flag F2 is set to “0”. Accordingly, theprocessor 31 proceeds to Act 13 and counts up the second counter t.Thereafter, in a case where it is determined that the instruction to endpositioning is not made, the processor 31 returns to Act 4 and executesprocessing in and after Act 4 again.

As a result, the processor 31 records “435” as the first ID, “−89” asthe RSSI, “435:1.0” as the occupation ratio, “−20” as the total anglesum, and “1.0” as the moving amount, respectively, in the third table333 in association with the time “10:10:14”. The occupation ratio isequal to or greater than the threshold value and thus, the processor 31records “435” as the second ID.

In this case, the second ID detected first by retrieving the third table333 is “435” recorded in association with the time “10:10:13” andcoincides with the second ID “435” recorded in association with the time“10:10:14”. Accordingly, the processor 31 proceeds to Act 10. Even atthis point in time, the second flag F2 is set to “0”. Accordingly, theprocessor 31 proceeds to Act 13 and counts up the second counter t.Thereafter, in a case where the instruction to end positioning is notmade, the processor 31 returns to Act 4 and executes the processing inand after Act 4 again.

When the time T reaches “10:10:15”, the beacon ID included in the beaconsignal whose the RSSI indicates the largest value “−89” at that time Tchanges to “436” of the base station 10B. As a result, the processor 31records “436” as the first ID, “−89” as the RSSI, “10” as the totalangle sum, and “1.5” as the moving amount, respectively, in the thirdtable 333 in association with the time “10:10:15”. The first IDs whichbecome the computation target for the occupation ratio are four beaconIDs of “435” of the base station 10A and one beacon ID of “436” of thebase station 10B. Accordingly, the processor 31 records “435:0.8,436:0.2” as the occupation ratio. Also, in this case, the occupationratio of the base station 10A is equal to or greater than the thresholdvalue and thus, the processor 31 records “435” as the second ID.

Similarly, the processor 31 records the first ID, the RSSI, theoccupation ratio, total angle sum, and the moving amount in the thirdtable 333 in association respectively with the time “10:10:16”,“10:10:17”, and “10:10:18”. Also, at time “10:10:18”, the occupationratio of the beacon ID “436” is equal to or greater than the thresholdvalue and thus, the processor 31 records “436” as the second ID. In thiscase, as a result of retrieving the third table 333 in Act 22, thesecond ID detected first is “435” recorded in association with the time“10:10:15” and thus, the second IDs are not coincident with each other.That is, the processor 31 determines that the determination result inAct 23 is “NO” and proceeds to Act 24. In Act 24, the processor 31counts up the counter n by “1”. That is, the value of counter n becomes“1”.

As Act 25, the processor 31 specifies an n-th neighboring time Tn. The“n” is the value of counter n. Specifically, the processor 31 retrievesthe records of the third table 333 retroactively from the time T andacquires the second ID detected first. The processor 31 extracts all therecords, in which the same ID as the second ID is recorded as the firstID, from the third table 333 at the time before time T. The processor 31sets the time of a record having the largest RSSI among the extractedrecords as the neighboring time Tn.

That is, the second ID detected first retroactively from time “10:10:18”is “435” at time “10:10:15”. Accordingly, five records, in which thefirst ID “435” is recorded and which are associated with the time“10:10:10” to the time “10:10:14”, are extracted from the third table333. Among the five records, the largest RSSI is the RSSI “−80” of therecord at time “10:10:10”. Accordingly, the time “10:10:10” of therecord having the largest RSSI becomes the first neighboring time T1.

When the neighboring time T1 is specified, as Act 26, the processor 31stores the neighboring time T1 in the volatile memory area of the mainmemory 32. Next, as Act 27, the processor 31 determines whether thevalue of the counter n is equal to or greater than “2” or not. In a casewhere it is determined that the value of the counter n is less than “2”(NO in Act 27), the processor 31 proceeds to Act 10 of FIG. 7.

At time “10:10:18”, the counter n is “1”. Accordingly, the processor 31proceeds to Act 10 of FIG. 7. Even at this point in time, the secondflag F2 is set to “0”. Accordingly, the processor 31 proceeds to Act 13and counts up the second counter t. Thereafter, in a case where theinstruction to end positioning is not made, the processor 31 returns toAct 4 and executes the processing in and after Act 4 again.

As a result, the processor 31 records “436” as the first ID, “−82” asthe RSSI, “436:1.0” as the occupation ratio, “436” as the second ID,“90” as the total angle sum, and “1.2” as the moving amount,respectively, in the third table 333 in association with the time“10:10:19”.

Thereafter, similarly, the processor 31 records the first ID, the RSSI,the occupation ratio, the total angle sum, and the moving amount in thethird table 333 in association respectively with the time “10:10:20”,“10:10:21”, “10:10:22”, and “10:10:23”. Also, at time “10:10:20”, theoccupation ratio of the beacon ID “436” is equal to or greater than thethreshold value and thus, the processor 31 records “436” as the secondID. Similarly, at time “10:10:23”, the occupation ratio of the beacon IDof “437” equal to or greater than the threshold value and thus, theprocessor 31 records the second ID “437”.

When the second ID “437” is recorded in association with the time“10:10:23”, in Act 23, it is determined that the second IDs are notcoincident with each other. As a result, the processor 31 proceeds toAct 24 and counts up the counter n by “1”. That is, the value of thecounter n becomes “2”.

As Act 25, the processor 31 specifies second neighboring time T2.Specifically, the second ID detected first retroactively from time“10:10:23” is “436”. Accordingly, five records, in which the first ID“436” is recorded and which are associated with the time “10:10:15” tothe time “10:10:19”, are extracted from the third table 333. Among thefive records, the largest RSSI is the RSSI “−79” of the record at time“10:10:17”. Accordingly, the time “10:10:17” of the record having thelargest RSSI becomes the second neighboring time T2.

Here, the processor 31 realizes the determination unit by executingprocessing of Act 8, Act 9, and Act 21 to Act 26.

When the second neighboring time T2 is stored in the volatile memoryarea of the main memory 32 in Act 26, the processor 31 determines thatthe determination result in Act 27 is YES and proceeds to Act 28.

In Act 28, the processor 31 sets the relative coordinates (PDRx, PDRy)of the positioning target 50 at the neighboring time T(n−1), whichcorresponds to the first time one before the latest neighboring time Tnwhich is the second time, as the first base point of the relativecoordinate system. The processor 31 replaces the relative coordinates(PDRx, PDRy), which are set as the first base points of the relativecoordinate system, with the absolute coordinates (X, Y) of the basestation 10 that transmits the strongest beacon signal at the neighboringtime T(n−1). Similarly, the processor 31 sets the relative coordinates(PDRx, PDRy) of the positioning target 50 at the latest neighboring timeTn, which is the second time, as the second base point of the relativecoordinate system. The processor 31 replaces the relative coordinates(PDRx, PDRy), which are set as the second base point of the relativecoordinate system, with the absolute coordinates (X, Y) of the basestation 10, which transmits the strongest beacon signal at theneighboring time Tn.

In the present operation example, the latest neighboring time (secondtime) T2 is “10:10:17” and the neighboring time (first time) T1 whichcorresponds to the time one before time “10:10:17” is “10:10:10”.Accordingly, the relative coordinates (PDRx1, PDRy1) of the positioningtarget 50 when it is the time T1 (“10:10:10”) become the first basepoint of the relative coordinate system. The relative coordinates(PDRx8, PDRy8) of the positioning target 50 when it is the time T2(“10:10:17”) become the second base point of the relative coordinatesystem. The base station that transmits the strongest beacon signal attime T1 (“10:10:10”) is the base station 10A and the absolutecoordinates of the base station 10A are (X10, Y10). The base stationthat transmits the strongest beacon signal at time T2 (“10:10:17”) isthe base station 10B and the absolute coordinates of the base station10B are (X20, Y20).

Accordingly, in Act 28, the processor 31 records an absolute coordinates(X10, Y10) in association with the time T1 (“10:10:10”) of the fourthtable 334 so that the relative coordinates (PDRx1, PDRy1) when it is thetime T1 (“10:10:10”), relative coordinates of the first base point, isreplaced with the absolute coordinates (X10, Y10). Similarly, theprocessor 31 records the absolute coordinates (X20, Y20) in associationwith the time T2 (“10:10:17”) of the fourth table 334 so that therelative coordinates (PDRx8, PDRy8) at time T2 (“10:10:17”), relativecoordinates of the second base point, is replaced with the absolutecoordinates (X20, Y20).

When the processing of Act 28 is ended, as Act 29, the processor 31calculates a scale magnification d and a rotational directiondisplacement Δθ for converting the relative coordinates into theabsolute coordinates. That is, the processor 31 calculates the scalingmagnification d by the following equation (1) and calculates thedisplacement Δθ in a rotational direction by the following equation (2),based on the relative coordinates (PDRx1, PDRy1) of the first basepoint, the relative coordinates (PDRx8, PDRy8) of the second base point,the absolute coordinates (X10, Y10) of the first base point, theabsolute coordinate (X20, Y20) of the second base point. In the equation(1), contents within the brackets [ ] mean that the contents arecontained in route symbols on the left side of the brackets.

d=√[(X20−X10)²+(Y20−Y10)²]√[(PDRx8−PDRx1)²+(PDRy8−PDRy1)²]  (1)

Δθ=tan⁻¹[(Y20−Y10)/(X20−X10)]−tan⁻¹[(PDRy8−PDRy1)/(PDRx8−PDRx1)]  (2)

Next, as Act 30, the processor 31 converts the position of thepositioning target 50 in each time (“10:10:11” to “10:10:16”) within atime period from the time T1 (“10:10:10”) to time T2 (“10:10:17”), a therelative coordinates (PDRx, PDRy) of the midpoints, into the absolutecoordinates (X, Y), by the following equations (3) and (4) using thescaling magnification d and the rotational direction displacement Δθ.

X=d(PDRx cos Δθ−PDRy sin Δθ)  (3)

Y=d(PDRx sin Δθ+PDRy cos Δθ)  (4)

The processor 31 records the absolute coordinates (X, Y) obtained bybeing converted from the relative coordinates (PDRx, PDRy) of each time(“10:10:11” to “10:10:16”) within the time period in association withthe time (“10:10:11” to “10:10:16”) of the fourth table 334.

Here, the processor 31 realizes a conversion unit by executingprocessing of Act 28 to Act 30.

As the Act 31, the processor 31 causes the display device 35 to displaya trajectory display screen 70 (see FIG. 9) representing the trajectoryof the positioning target from time T1 to time T2, based on the absolutecoordinates (X, Y) for each time stored in the fourth table 334.

FIG. 9 is an example of the trajectory display screen 70. In the exampleof FIG. 9, the trajectory of the positioning target 50 from thecoordinates (X10, Y10) which becomes the first base point at time T1(“10:10:10”) to the coordinates (X20, Y20) which becomes the second basepoint at time T2 (“10:10:17”) is depicted by points indicating thecoordinates which become the midpoint of each time (“10:10:11” to“10:10:16”) and arrows connecting the points. Although not specificallydepicted in FIG. 9, a map of the positioning area 60 is also displayedon the trajectory display screen 70.

When processing of Act 31 is ended, as Act 32, the processor 31 sets thesecond flag F2 to “1”. Thereafter, the processor 31 proceeds to Act 10.At this point in time, the second flag F2 is updated with “1”.Accordingly, the processor 31 executes processing of Act 11 and Act 12.

That is, as Act 11, the processor 31 calculates a tentative position inthe absolute coordinate system of the positioning target 50 fromrelative movement data aftertime T2 (“10:10:17”) at which the secondbase point is set. Specifically, the processor 31 acquires the totalangle sum “80°” of the relative movement data and the moving amount “1.0m” of the relative movement data stored in association with the time“10:10:18” from the third table 333. Further, the processor 31 obtainsthe direction relative to the absolute coordinates at time “10:10:17” byadding Δθ obtained by the equation (2) to the total angle sum “30°”stored in association with the time “10:10:17” in the third table 333.The processor 31 calculates the coordinates (X20+α1, Y20+β1) of a point,which is moved from the absolute coordinate (X20, Y20) stored in thefourth table 334 in association with the time “10:10:17” by the movingamount “1.0 m”, in a direction [(Δθ+30)+50] obtained by adding adifference “50°” in the total angular sum between time “10:10:17” andtime “10:10:18” to the direction (Δθ+30) with respect to the absolutecoordinate at time “10:10:17”, as the tentative position coordinates.The processor 31 records the tentative position coordinates (X20+α1,Y20+β1) in association with the time “10:10:18” of the fourth table.Next, the processor 31 acquires the total angle sum “90°” and the movingamount “1.2 m” of the relative movement data stored in association withthe time “10:10:19” from the third table 333. The processor 31calculates the coordinates (X20+α1, Y20+β1) of a point, which is movedfrom the tentative position coordinates (X20+α1, Y20+β1) stored inassociation with the time “10:10:18” in the fourth table 334 by themoving amount “1.0 m”, in a direction [[Δθ+30)+50]+10] obtained byadding a difference “10°” in the total angular sum between time“10:10:18” and time “10:10:19” to the direction [(Δθ+30)+50] withrespect to the tentative position coordinate at time “10:10:18”, as thetentative position coordinates. The processor 31 records the tentativeposition coordinates (X20+α2, Y 20+β2) in association with the time“10:10:19” of the fourth table. Thereafter, the processor repeatsprocessing of obtaining the tentative position coordinates for each timein the same manner as described above until time “10:10:23”corresponding to the value of the second counter t is reached. Here, theprocessor 31 realizes a tentative unit by executing processing of Act11.

As Act 12, the processor 31 adds a trajectory representing a tentativeposition of the positioning target to the trajectory display screen 70based on the coordinates (X, Y) after time T2 (“10:10:17”) stored in thefourth table 334.

FIG. 10 is an example of the trajectory display screen 70 to which thetrajectory representing the tentative position is added. In the exampleof FIG. 10, the trajectory representing the tentative position of thepositioning target is indicated by the dashed line.

When processing of Act 11 and Act 12 is ended, the processor 31 proceedsto Act 13 and counts up the second counter t by “1”. Thereafter, in acase where the instruction to end positioning is not made, the processor31 returns to Act 4 and executes processing in and after Act 4 again.

As a result, the processor 31 records “437” as the first ID, “−89” asthe RSSI, “437:1.0” as the occupation ratio, “437” as the second ID, and“10” as the total angle sum, and “1.0” as the moving amount,respectively, in the third table 333 in association with the time“10:10:24”. At this time, the second flag F2 is set to “1” and thus,processing of Act 11 and Act 12 is executed. That is, the processor 31obtains the tentative position of the positioning target 50 at time“10:10:24” and adds the tentative position and the trajectory to thetrajectory display screen 70.

Thereafter, the processor 31 repeats the same processing. Accordingly,in processing of Act 25, when the third time T3 (“10:10:22”) for thebase station 10C having the beacon ID “427” is specified, the processor31 executes processing of Act 28 to Act 31. That is, the processor 31records the absolute coordinates (X30, Y30) in association with the timeT3 (“10:10:22”) of the fourth table 334 so that the relative coordinates(PDRx, PDRy) of the positioning target 50 at the third time T3 isreplaced with the absolute coordinates (X30, Y30) of the base station10C.

Furthermore, the processor 31 calculates the scale magnification d andthe rotational direction displacement Δθ for converting the relativecoordinates into the absolute coordinates. The processor 31 converts theposition of the positioning target 50 in each time (“10:10:18” to“10:10:21”) within a time period between time T2 (“10:10:17”) and timeT3 (“10:10:22”), the relative coordinates (PDRx, PDRy) of the midpoints,into the absolute coordinates (X, Y) and corrects the tentative positioncoordinates stored in association with each time (“10:10:18” to“10:10:21”) of the fourth table 334 to the absolute coordinates thereof.

In a case where the instruction to end positioning is input through theinput device 34, the processor 31 determines that the determinationresult in Act 14 is “YES” and ends information processing.

As described above, in the positioning system 100, the positioningtarget 50 carries the mobile station 20 capable of receiving radio wavesof the beacon signals transmitted from multiple base stations 10 spacedapart from each other. In the first table 331, the positioning server 30stores strength data of radio waves, which are transmitted and receivedrespectively between the mobile station 20 and each base station 10, intime series.

The positioning system 100 measures the position of the positioningtarget 50 by the PDR using the mobile station 20. The positioning server30 stores data of the relative coordinate system, which is related tothe movement of the positioning target 50, in the second table 332 intime series.

Furthermore, the positioning server 30 executes the followingoperations. That is, the positioning server 30 determines the time atwhich the positioning target 50 comes closest to each base station 10,based on time series strength data stored in the first table 331.Between a first neighboring time when the positioning target 50 becomesclosest to a first base station 10 and a second neighboring time whenthe positioning target 50 becomes closest to a second base station 10,the positioning server 30 converts data of the relative coordinatesystem stored in the second table 332 into the absolute coordinatesystem set at the first base station 10.

Therefore, according the positioning system 100 including thepositioning server 30, it is possible to determine the absolute positionof the positioning target 50 from positional data of the positioningtarget 50 obtained based on the relative coordinate system. In thiscase, there is no need to perform a predetermined operation on themobile station 20 when the positioning target comes close to the basestation 10. That is, a manual operation by a user is not needed andthus, the positioning server 30 and the positioning system 100 aresimpler and use thereof is not limited to manual systems. In addition,there is no need to reduce the distance that the radio waves travel fromthe base station 10 and thus, it is possible to perform positioning withhigh reliability.

The positioning server 30 obtains the ratio of the base station 10 forwhich strength data becomes the largest within a predetermined time.When the ratio exceeds a predetermined threshold value, the base station10 is set as a determination target, and the timing when the strengthdata of radio becomes the largest is recorded. Accordingly, even whenthe signal strength of the radio wave transmitted from the base station10 is temporarily high at an unexpected place distant from the basestation 10, this received signal strength information can be discardedso that it is possible to detect a position of the base station 10 withhigh accuracy.

The positioning server 30 can calculate the tentative position in theabsolute coordinate system of the positioning target 50 based on therelative coordinate system data stored in the second table 332 inassociation with the time later than the second time. The calculatedtentative position is the latest position of the positioning target 50.Accordingly, a trajectory can be obtained by adding the tentativeposition to the absolute position of the positioning target 50 in theabsolute coordinate system having the particular base station set as thebase point when the positioning target 50 previously came closest to theparticular base station 10.

The tentative position is corrected every time the positioning targetcomes closest to another one of the base stations 10. Accordingly,reliability of positioning is not impaired.

In the following, a modification of the example embodiment describedabove will be described.

In the example embodiment described above, the base station 10 transmitsa beacon signal and the mobile station 20 receives a beacon signal. Inthe modification, the mobile station 20 transmits a beacon signal andthe base station 10 receives a beacon signal. In this case, the basestation 10 may transmit data relating to radio wave reception strengthof the beacon signal to the positioning server 30 via the access point41, or may transmit the data to the positioning server 30 via the accesspoint 41 through the mobile station 20.

In the example embodiments described above, the evaluation target timefor computing the occupation ratio is set to 5 seconds. However, theevaluation target time may be other lengths. Similarly, a thresholdvalue for the occupation ratio is not limited to 80% and may be othervalues.

In the example embodiments described above, the trajectory indicatingthe movement of the positioning target 50 is displayed. However, thepositioning system 100 may detect the absolute position of thepositioning target 50 and not display a trajectory. In this case,processing steps of Act 12 of FIG. 7 and Act 31 of FIG. 8 are omitted.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms. Furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A positioning device, comprising: a processorconfigured to: calculate a first neighboring time at which a mobiledevice becomes closest to a first base station in a plurality of basestations based on received signal strength data and a second neighboringtime at which the mobile device becomes closest to a second base stationin the plurality of base stations; and convert relative movement datainto position coordinates data specifying an absolute position of themobile device in an absolute coordinate system using the location of thefirst base station as a reference point from the first neighboring timeto the second neighboring time, wherein the received signal strengthdata is in a time series according to time information from the mobiledevice and includes a received signal strength indicator according to asignal strength between the mobile device and each of the plurality ofbase stations, and the relative movement data is received from themobile device in time series within a relative coordinate system.
 2. Thepositioning device according to claim 1, wherein the processor isfurther configured to: compute an occupation ratio for each base stationin the plurality of base stations for which the received signal strengthdata is received within a predetermined time, and determine the mobiledevice is closest to a particular base station in the plurality of basestations when the occupation ratio for that particular base stationexceeds a predetermined threshold value.
 3. The positioning deviceaccording to claim 1, wherein the processor is further configured tocalculate a tentative position of the mobile device in the absolutecoordinate system based on the relative movement data in associationwith each time subsequent to the second neighboring time.
 4. Thepositioning device according to claim 3, wherein the processor isfurther configured to: determine a third neighboring time at which themobile device becomes closest to a third base station in the pluralityof base stations; and convert the relative movement data from the secondneighboring time to the third neighboring time into position coordinatesdata specifying an absolute position of the mobile device in theabsolute coordinate system, and replace the tentative position of themobile device with the absolute position.
 5. The positioning deviceaccording to claim 4, further comprising: a display screen configured todisplay a trajectory of the mobile device, the trajectory including acalculated absolute position of the mobile device and a calculatedtentative position of the mobile device at times prior to the currenttime.
 6. The positioning device according to claim 1, wherein theplurality of base stations are signal beacons transmitting radio wavesto the mobile device, and the received signal strength indicator is setaccording to a strength of the radio waves received at the mobiledevice.
 7. The positioning device according to claim 1, wherein themobile device transmits radio waves to the plurality of base stations,and the received signal strength indicator is set according to astrength of the radio waves received at a base station.
 8. A positioningsystem, comprising: a plurality of base stations distributed within apositioning area, each of the base stations being at a location withknown coordinates within an absolute coordinate system; a mobile deviceconfigured to: transmit signals to the base stations and receive signalsfrom the base stations; and estimate a moving direction and a movingvelocity of the mobile device from sensor data to generate relativemovement data; and a positioning server configured to: calculate a firstneighboring time at which the mobile device becomes closest to a firstbase station in the plurality of base stations based on received signalstrength data and a second neighboring time at which the mobile devicebecomes closest to a second base station in the plurality of basestations; and convert relative movement data from the mobile device intoposition coordinates data specifying an absolute position of the mobiledevice in an absolute coordinate system using the first base station asa reference point from the first neighboring time to the secondneighboring time, wherein the received signal strength data is in a timeseries according to time information from the mobile device and includesa received signal strength indicator according to a signal strengthbetween the mobile device and each of the plurality of base stations,and the relative movement data is received from the mobile device intime series within a relative coordinate system.
 9. The positioningsystem according to claim 8, wherein the processor is further configuredto: compute an occupation ratio for each base station in the pluralityof base stations for which the received signal strength data is receivedwithin a predetermined time, and determine the mobile device is closestto a particular base station in the plurality of base stations when theoccupation ratio for that particular base station exceeds apredetermined threshold value.
 10. The positioning system according toclaim 8, wherein the processor is further configured to calculate atentative position of the mobile device in the absolute coordinatesystem based on the relative movement data for times subsequent to thesecond neighboring time.
 11. The positioning system according to claim10, wherein the processor is further configured to: determine a thirdneighboring time at which the mobile device becomes closest to a thirdbase station in the plurality of base stations; and convert the relativemovement data from the second neighboring time to the third neighboringtime into position coordinates data specifying an absolute position ofthe mobile device in the absolute coordinate system, and replace thetentative position of the mobile device with the absolute position. 12.The positioning system according to claim 11, further comprising: adisplay screen configured to display a trajectory of the mobile device,the trajectory including a calculated absolute position of the mobiledevice and a calculated tentative position of the mobile device at timesprior to the current time.
 13. The positioning system according to claim8, wherein the plurality of base stations are signal beaconstransmitting radio waves to the mobile device, and the received signalstrength indicator is set according to a strength of the radio wavesreceived at the mobile device.
 14. The positioning system according toclaim 8, wherein the mobile device transmits radio waves to theplurality of base stations, and the received signal strength indicatoris set according to a strength of the radio waves received at a basestation.
 15. A positioning method, comprising: calculating a firstneighboring time at which a mobile device becomes closest to a firstbase station in a plurality of base stations based on received signalstrength data and a second neighboring time at which the mobile devicebecomes closest to a second base station in the plurality of basestations; and converting relative movement data into positioncoordinates data specifying an absolute position of the mobile device inan absolute coordinate system using the first base station as areference point from the first neighboring time to the secondneighboring time, wherein the received signal strength data is in a timeseries according to time information from the mobile device and includesa received signal strength indicator according to a signal strengthbetween the mobile device and each of the plurality of base stations,and the relative movement data is received from the mobile device intime series within a relative coordinate system.
 16. The positioningmethod according to claim 15, further comprising: computing anoccupation ratio for each base station in the plurality of base stationsfor which the received signal strength data is received within apredetermined time; and determining the mobile device is closest to aparticular base station in the plurality of base stations when theoccupation ratio for that particular base station exceeds apredetermined threshold value.
 17. The positioning method according toclaim 15, further comprising: calculating a tentative position of themobile device in the absolute coordinate system based on the relativemovement data in association with each time subsequent to the secondneighboring time.
 18. The positioning method according to claim 17,further comprising: determining a third neighboring time at which themobile device becomes closest to a third base station in the pluralityof base stations; and converting the relative movement data from thesecond neighboring time to the third neighboring time into positioncoordinates data specifying an absolute position of the mobile device inthe absolute coordinate system, and replacing the tentative position ofthe mobile device with the absolute position.
 19. The positioning methodaccording to claim 18, further comprising: displaying a trajectory ofthe mobile device, the trajectory including a calculated absoluteposition of the mobile device and a calculated tentative position of themobile device at times prior to the current time.
 20. The positioningmethod according to claim 15, wherein the plurality of base stations aresignal beacons transmitting radio waves to the mobile device, and thereceived signal strength indicator is set according to a strength of theradio waves received at the mobile device.